1. Field of the Invention
The present invention comprises an apparatus for supporting a visual image projection device. An aspect of the present invention is a stacking stand which adjustably supports a slide projector for rotation in three degrees of freedom to align an image projected by the slide projector with a target image or area.
2. Description of the Prior Art
Audio-visual presentations are widely used for many purposes. Such presentations often include what is commonly referred to as "slide shows" or the like, i.e. visual depiction of information and images contained on slides by means of slide projectors having a light projecting lamp. Such "slide shows" are often used for business, education and othe related communication purposes. The slides in this kind of presentation primarily depict information of value to the audience from an informational or educational standpoint. However, such presentations are made more effective if they simultaneously entertain or please the audience.
Historically, slide presentations involved a single projector which projected slides alternately onto a screen. In such an arrangement, intervals of no light appeared on the projection screen while the projector automatically advanced to the next slide. In recent years, however, "dissolve" presentations utilizing two projectors focused on a single screen have become popular. The lamps of the projectors in a dissolve presentation are controlled by a control unit for alternately projecting images from the projectors onto the screen. The control unit also serves to dissolve the images from one of the projectors, i.e. fade the image out, as the image from the other projector is brought up on the screen. Thus, a viewer sees the image on the screen change before his very eyes in a smooth sequence without any intervening break or dark interval on the screen. It is not uncommon in such presentations to utilize a plurality of screens each having more than one projector focused on it. For example, dissolve presentations utilizing up to ten screens are not unusual. These multi-screen presentations are also known by the term "multi-image" presentations.
It is a major problem in dissolve presentations to keep the plural images appearing on the screen aligned or superimposed with one another. In this regard, it is extremely important that the projectors be adjustably and firmly supported to achieve proper alignment of their images. Since the projectors are often located at extremely large distances from the screen, a small error or deviation at the projector results in a large error or deviation of the image on the screen. Thus, the support member for the projectors must be capable of precisely positioning the projectors relative to the screen. Such a support member should also be simple and easy to operate since the set-up and dismantling of a multi-image presentation is complex and difficult.
Various prior art products have been developed for adjustably supporting a plurality of projectors relative to a screen to allow alignment of their images. One such type of prior art stands is generically known as "piggy-back" stands. In such stands, the first projector is placed on a table or other flat surface in a position where it projects a target image onto the screen. A piggy-back stand is provided having a plurality of feet which support a mounting bracket on which the second projector is mounted. The second projector is positioned by the stand above the level of the first projector. The piggy-back stand is then manually moved horizontally to adjust the yaw position of the second projector. Thereafter, the projectors leveling feet are moved to adjust the pitch and roll positions of the projector to achieve alignment of the images on the screen.
One disadvantage of piggy-back stands is that they are dificult to adjust to achieve image alignment. Since the alignment of the stands is basically done manually, i.e. by simply moving the stand and the projectors own controls until the second projector supported thereon has its image aligned with the target image, it is difficult to precisely adjust such a device. In addition, a piggyback stand, if jostled or otherwise moved, will easily lose its image alignment. This requires a lengthy readjustment and realignment of the second projector.
Other prior art projector stands are known which allow a more precise adjustment of the projector while also maintaining that adjustment to a greater degree than is possible with "piggy-back" stands. One such stand is known which allows for adjustment of the projector along three mutually perpendicular axes, i.e. along pitch, roll and yaw axes. However, this stand as previously known exhibits a number of problems. It is often extremely difficult to adjust for a number of reasons. First, the projector adjustment controls are difficult to reach and operate. In addition, the weight of the projector must sometimes be supported by the operator when the stand is unlocked, thereby increasing the difficulty in making the proper adjustments. This problem is especially acute to an inexperienced operator who is not expecting the weight of the projector when the locking controls on the prior art stackers are released. Thus, the prior art stacker which adjusts the pitch, roll and yaw of a projector is difficult and time consuming to use.